A. Field of the Disclosure
This disclosure relates generally to pipes and, more particularly, to methods and apparatus for joining pipes.
B. Background
Pipe used for underground work is typically provided with a flared bell at one end and a spigot at the opposite end. The inner diameter of the flared bell end is greater than the outer diameter of the spigot end. This allows lengths of pipe to be joined end-to-end by inserting the spigot end of one pipe into the flared bell end of another pipe. Since the inner diameter of the flared bell is greater than the outer diameter of the spigot, an annular space is created therebetween. The annular space is typically sealed by various means in order to prevent fluid leakage when the pipes are connected together. Unfortunately, shifting and settling of the earth may cause deflection between joined pipes which can lead to fluid leakage as well as damage to the pipes themselves. In order to accommodate this shifting and settling, several means have been employed.
Conventional push-on joints have a stationary gasket inside the flared bell of the pipe and seal against the spigot. Deflection of the spigot in the socket occurs due to the clearances provided between the socket and spigot. Typically a tight joint, i.e., with the bell at minimum tolerance inside diameter and the spigot at maximum tolerance outside diameter will deflect considerably less than a loose joint with the minimum spigot and maximum bell. However, stationary gaskets frequently catch on the spigot during insertion of the spigot into the socket, resulting in a bad seal.
Other means have also been employed to accommodate the shifting and settling and also to accommodate the shaking during an earthquake. Some joints utilize a ball and socket joint, wherein a stationary gasket in the large flared socket seals against a spherically shaped spigot. The spherically shaped spigot is a separate casting and must be attached to the straight spigot by some mechanical means. This creates potential weaknesses in the pipe, increases the cost of manufacturing, and increases the complexity of assembly. Flexible expansion joints are also used to accommodate these large deflections. In all cases these flexible expansion joints require a raised rib or stop on the spigot to prevent separation and a unitary ball for the gasket to seal upon. Because many flexible expansion joints comprise two separate ball joints and a middle expansion joint, the ball joints have to be connected to a pipe end or spigot through a flange joint or usually a mechanical joint with restraint. That is, the ends of the ball joints have either a Flange or an MJ joint which can then be connected to a pipe spigot, introducing additional potential points of mechanical weakness and further complexity of assembly.